1. Field of the Invention
The present invention relates to a pressure sensor for measuring various kinds of pressure and atmospheric pressure which are input signals to be utilized mainly in various control for a vehicle, and a chip therefor.
2. Discussion of Background
As an example of conventional pressure sensors is known the one which is disclosed in Japanese Unexamined Patent Publication No. 199653/1991. The pressure sensor and its surroundings in the publication is shown in FIG. 7.
In FIG. 7, reference numeral 1 designates an intake pipe, reference numeral 2 designates an injector for injecting fuel, reference numeral 3 designates a throttle valve which operates according to the degree to which a driver pushes an accelerator, pedal, reference numeral 4 designates a pressure sensor, reference numeral 5 designates a computer, reference numeral 6 designates a three port solenoid valve which directs the pressure in the intake pipe 1 or an atmospheric pressure to the pressure sensor 4 by performing a switching operation in accordance with a command from the computer 5, and reference numeral 7 designates an engine.
FIGS. 8(a) and 8(b) are schematic views showing essential parts in the pressure sensor 4, and FIG. 9 is a diagram showing an electric equivalent circuit in the pressure sensor. In those Figures, reference numeral 8 designates a pressure-sensitive element wherein resistors 10 are provided in a Wheatstone bridge arrangement on a diaphragm 9 which is made from thin silicon semiconductor. In the pressure-sensitive element 8, the diaphragm 9 is deformed by a pressure medium introduced through a nipple 11 to change the resistance value of the resistor 10, and an output signal which is proportional to a pressure from the pressure medium is fed to the computer from an output terminal.
The circuit which is shown in FIGS. 8(a) and 8(b), and FIG. 9 will be explained in more detail. Reference numeral 12 designates a hybrid integrated circuit wherein thick film resistors (not shown) are formed on e.g. an alumina substrate 13 by printing. The integrated circuit 12 has chip capacitors 14 mounted thereinto, and has other devices arranged therein, the other devices including e.g. an integrated circuit chip 16 which has e.g. operational amplifiers 15 built therein to amplify a signal from the pressure-sensitive element 8 and to perform temperature compensation. Reference numerals 17 and 18 designate temperature compensating adjustment circuits.
The pressure-sensitive element 8, the hybrid integrated circuit 12 and others are provided in the pressure sensor 4 in that manner.
Now, the operation of the device shown in FIG. 7 will be explained.
External air is taken into through an air cleaner, not shown, and the air is introduced into the engine 7 through the intake pipe 1 and an intake manifold. The injector 2 injects fuel into the intake manifold, and compression and combustion are carried out in the engine 7 to obtain a power source for the internal engine. The amount of fuel injected from the injector 2 is calculated in the computer 5, depending on the amount of air taken from the intake pipe 1 and other operational information. The computer 5 has various operational factors input thereinto. In the operational factors is involved a pressure in the intake pipe 1 and an atmospheric pressure. The pressure in the intake pipe and the atmospheric pressure is measured by the same pressure sensor 4. Since both pressures can not be measured at the same time, the three port solenoid valve 6 is arranged in a tube through which a gas to be measured is directed to the pressure sensor 4. By switching the valve 6, both pressures can be measured respectively. In the device disclosed in the Japanese Unexamined Patent Publication, when the throttle valve 3 is fully closed on deceleration, the three port solenoid valve 6 is switched to introduce atmosphere into the pressure sensor 4. In this way, the pressure in the intake pipe and an atmospheric pressure are measured by the single pressure sensor 4.
The pressure sensor 4 is constituted mainly by the pressure-sensitive element 8 and the hybrid integrated circuit 12. When a pressure P arrives at the diaphragm 9 of the pressure-sensitive element 8 through the nipple 11 and deforms the diaphragm, changes in the values of the resistance in the four resistors 10 which are provided on the diaphragm 9 in the Wheatstone bridge arrangement appear. A signal caused by the change in the values of resistance is amplified by the operational amplifiers 15, is compensated in the temperature compensation circuits 17 and 18, and is fed to the computer 5 as an analog output which is accurately proportional to the pressure P.
Another example of the conventional devices is the system which is disclosed in Japanese Unexamined Patent Publication No. 205832/1986, and which reads a pressure in an intake pipe by a pressure sensor at specific operating conditions without a three port solenoid valve, and subjects the read pressure to compensatory calculation to see an approximate atmospheric pressure.
Another example is a system which measures an atmospheric pressure by a pressure sensor for measuring a pressure in an intake pipe before cranking just after an ignition switch is turned on.
In addition, there is an example wherein a pressure sensor for an intake pressure and an atmospheric pressure sensor are individually provided.
The conventional pressure measuring systems as stated earlier create the following problems:
Specifically, in the one shown in FIG. 7, although it is enough to provide the single pressure sensor, the three port solenoid valve 6 is required to selectively introduce the pressure in the intake pipe and external air into the single pressure sensor. As a result, the pressure measuring system including piping gets large, which is against space savings and involves high cost.
The one disclosed in Japanese Unexamined Patent Publication No. 205832/1986 could not obtain atmospheric pressure information when the information is required. It can not obtain accurate atmospheric pressure information either because the obtained atmospheric pressure is approximate value. This arrangement creates a problem in that it is impossible to carry out fine control.
The system which measures an atmospheric pressure before cranking involves a problem in that the atmospheric pressure can not be always measured at every operation mode before cranking after turning on the ignition switch (because resetting an IC is required at some operation modes).
The arrangement wherein the pressure sensor for a pressure in the intake pipe and the atmospheric pressure sensor are individually provided creates a problem in that cost rises necessarily.